A vehicle with a turbocharger coupled to its engine may experience a condition known as “turbo lag” during engine operation. Since the turbocharger is powered by exhaust gas energy, a delay (e.g., turbo lag) occurs in response to a request for increased torque when the turbine and/or compressor are not at speeds at which they may supply sufficient boost pressure to increase the engine torque.
The inventors herein have recognized that the above problem can be at least partly addressed by a boosted engine system that uses a binary flow turbine. In one example, turbo lag is reduced by a method comprising: in response to a tip-in, adjusting an opening of a scroll valve coupled to an outer scroll of a multi-scroll exhaust turbine to reduce turbo lag, and adjusting an amount of exhaust gas recirculated to an engine intake based on the scroll valve opening.
In one example, in response to a tip-in, a scroll valve coupled to only an outer scroll of a multi-scroll exhaust turbine may be moved to a more closed position, such as to a fully closed position. The closing of the scroll valve may be based on the turbine speed at tip-in (e.g., based on a difference between the turbine speed at tip-in and the turbine speed desired based on torque demand at tip-in). For example, when the turbine speed at tip-in is lower, the scroll valve may be moved to a more closed position while when the turbine speed at tip-in is higher, the scroll valve may be moved to a less closed position. The scroll valve may be maintained at the closed position until the turbine speed is at or above a threshold speed (e.g., the desired speed). Then, as the turbine speed increases above the threshold speed, the scroll valve opening may be increased. By closing the scroll valve at lower turbine speeds, exhaust flow to the turbine is restricted to a narrow passage, causing the exhaust to flow at a higher pressure to the turbine inlet. This expedites turbine spool-up and resulting turbine power. By expediting turbo spooling, turbo lag is reduced and boost performance response to the tip-in is improved, in particular at low engine speeds and boost levels.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.